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Gas chromatography–mass spectrometry (GC–MS) with Cold EI is based on interfacing GC and MS with supersonic molecular beams (SMBs) along with electron ionization of vibrationally cold sample compounds in SMB in a fly‐through ion source (hence the name Cold EI). Cold EI improves all the central performance aspects of GC–MS, and in this paper, we focus on its improvement of signal‐to‐noise ratio (S/N) and limits of detection (LODs). We found that the harder the compound for analysis with standard EI, the greater the Cold EI gain in S/N and LOD. The lower LOD and higher S/N of Cold EI emerge from a few reasons: (a) similar ionization yield as standard EI, (b) enhanced abundance of molecular ions, (c) elimination of vacuum background noise, (d) elimination of ion source‐related peak tailing and degradation, (e) ability to lower the elution temperatures via the use of high column flow rates, and (f) greater range of thermally labile and low‐volatility compounds that can be analyzed. We demonstrate the superior S/N and lower LOD of Cold EI versus standard EI in a range of compounds, from the simple‐to‐analyze octafluoronaphthalene all the way to reserpine and an organo‐metallic compound that cannot be analyzed by standard EI. These compounds include methyl stearate, cholesterol, n‐C32H66, large polycyclic aromatic hydrocarbons, dioctyl phthalates, diundecyl phthalate, pentachlorophenol, benzidine, lambda‐cyhalothrin, and methidathion. The significantly lower Cold EI LODs that can be over 1000 times better than in standard EI further result in far superior response linearity and greater measurement dynamic range. [ABSTRACT FROM AUTHOR]

Open Probe is based on a vaporization oven mounted on a transfer line of a gas chromatograph mass spectrometer (GC/MS) which is connected to the MS ion source via a short flow restriction capillary. The probe oven is open to room air while having helium purge flow protection to eliminate or significantly reduce air leakage into the oven and MS ion source. Sample analysis can be as simple as touch (the sample), push (the sample holder) into the open probe oven, and have the results. Experiments were performed with a GC/MS with supersonic molecular beams and with a standard Agilent 5975 MSD. Powders and tablets analysis were performed by touching the sample with the bottom side of a melting point vial and inserting it into the open probe oven with total analysis cycle time of 10.1021/ac100834h

New methods for fast, sensitive, and informative pesticide analysis in food products are described. These methods are based on sampling with a novel direct sample introduction device (DSI), gas chromatographic analysis, and pesticide detection with the pulsed flame photometric detector (PFPD). Sampling with the DSI is based on introduction of blended fruit or vegetable in a small glass vial that retains the harmful nonvolatile residue and is disposed of after the analysis. The DSI-GC-PFPD combination provides several new features that are demonstrated and discussed: (a) Extract-free analysis is achieved with the DSI, which serves as an effective alternative to sample extraction and cleanup methods. (b) Faster analysis is achieved through the use of the DSI due to the reduction of the upper GC program temperature, since the low-volatility compounds are retained in the sample vial. (c) Relatively efficient and uniform DSI thermal extraction and PFPD detection can be achieved, allowing the use of internal standards for pesticide calibration. (d) Higher sensitivity is provided by the PFPD as well as through the use of the DSI for sampling larger volumes of extract solutions. (e) Sulfur interference is eliminated with the PFPD in its phosphorus-selective detection mode, using software exploiting differences in S and P delayed pulsed flame emission time dependence. (f) Sulfur pesticides are effectively analyzed by the PFPD in its sulfur-selective detection mode at the usual required levels and with less matrix interference than with NPD in the nitrogen mode. (g) Simultaneous sulfur and phosphorus pesticide analysis is demonstrated, including heteroatom identification and the provision of P and S atom ratio information in the analyzed pesticide.

We describe here a novel water electrolyzer-powered flame ionization detector (EFID), characterized by enhanced portability, reduced cost of operation and improved safety of operation and storage. A conventional FID operates with a hydrogen diffusion flame, which has a central flow of pure hydrogen and column effluents, surrounded by a much higher coaxial flow of pure air. In contrast, the EFID is based on the combustion of a premixed (unseparated), hydrogen and oxygen, stoichiometric gas mixture. This premixed gas mixture is provided by a simple water electrolyzer with low power and water consumption, without separation, compression, or pressure stabilization of the hydrogen and oxygen. The EFID is very similar to FID with two minor modifications: (a) The flame tip must have a narrow hole ([approximately]250 [[micro]meter]) to prevent flame flash-backs. (b) The entire detector structure is maintained above 100 [degrees] C to prevent water condensation due to the lack of diluting air. The EFID sensitivity is similar to that of the FID, and up to twice improved detectivity is demonstrated with the EFID. The flame chemical ionization yield of the EFID linearly increases with the electrolysis current The EFID response is linear over almost 6 orders of magnitude. The response is selective to carbon compounds where the response in aliphatic compounds is [approximately]30% lower than with aromatic compounds, and no observable difference for N-, S-, P-, and Cl-containing compounds. The use of splitless solvent injections with a megabore column (0.53 mm i.d.) quenches the flame. This flame extinction is eliminated by the use of a miniature air pump during the solvent elution time. Typical electrolyzer operating parameters are current of 1.5 A, 12 mL/day water consumption and 4 W electrolyzer power requirements. Thus, a relatively small size water electrolyzer can provide the total gas consumption of the EFID for up to 40 days before water replenishing is required. This EFID can also be operated either as an EFID or as an FID, simply by replacing the gas sources.

The pulsed flame photometric ionization detector (PFPID) is designed for the simultaneous selective detection of molecules containing carbon, sulfur, phosphorus, or nitrogen atoms using gas chromatography (GC). The PFPID is based on a pulsed flame which propagates from the igniter through the ionization and photometric chambers consecutively. The flame is then self-terminated and reignited after a few hundred milliseconds in a pulsed periodic fashion. Since the pulsed flame photometer works with a hydrogen-rich atmosphere, the GC eluting molecules are predominantly pyrolyzed and only slightly combusted in the initial pulsed flame photometric chamber. These products are further combusted in the second pulsed flame ionization chamber, where the combustible gas mixture is separately optimized. The resulting electrons/ions are collected by an electrically isolated collector positively biased to 10 V. The addition of a pulsed flame ionization detector (PFID) to the pulsed flame photometric detector (PFPD) requires addition of negligible hardware (an isolated charge collector). It also requires the addition of a current-to-voltage converter and a double-gated instead of a single-gated amplifier for simultaneous PFPD-PFID work. The PFPID can be operated separately as either a pulsed FPD or a pulsed FID or simultaneously as both at the same H2/air gas flow rates. The simultaneous selective analysis of sulfur and organic compounds in gasoline, kerosene, and diesel fuel is demonstrated and discussed in terms of the various operational parameters. The performance of the PFPID is analyzed and compared to that of other sulfur and carbon simultaneous selective detection schemes.

The pulsed-flame photometer detector (PFPD) is based on a flame source and combustible gas flow rate that cannot sustain a continuous-flame operation. Thus, the ignited flame propagates back to the combustible gas mixture source and is self-terminated after the combustible gas mixture is burnt. The continuous gas flow creates addltional ignitions in a periodic fashion. The maln feature that characterizes the pulsed-flame photometer detector is the pulsed nature of the emitted light. Time domain information is added to the heteroatom specific emission with time-dependent emission being observed. In this paper we describe the PFPD and evaluate its performance as a gas chromatograph detector. The main advantages of the PFPD include improved detection sensitivity for sulfur and phosphorus, much higher selectivity against hydrocarbon molecules, lower gas consumption, reduced emission quenching, additional temporal information, and the ability to detect selectively other heteroatoms such as nitrogen or the simultaneous detection of sulfur and carbon. Points for further examination are the emission dependence on the column flow rate and combustion cell surface effects on the pulsed flame emission. The minimum detection levels achieved are 2 X [10.sup.-13] g S/s, 1 X [10.sup.-14] g P/s, 5 X [10.sup.-12] g N/s and 6 X [10.sup.-11] g C/s. The PFPD is unaffected by the injection of large amounts of solvent including aromatic solvents, and both sulfur and phosphorus can be detected and quantified at sub-ppb concentration levels. The sulfur concentration dependence of the PFPD is quadratic, and its response is independent of the structure of the sulfur-containing molecule. The detector response time is fast enough to closely resemble the flame lonization detector for both sulfur and phosphorus molecules resolved chromatographically on a narrow-bore column. The operation of the PFPD on either S, P, N, C single-element channels or S + P, S + C, P + N, or S + P + N multielement detection modes is described and presented., The advantages and diasadvantages of the operation of a pulsed flame photometer as a gas chromatography detector were derived. The photometer was evaluated based upon its performance in experiments involving the selective detection of sulfur, phosphorous, carbon and nitrogen by capillary gas chromatograpy. Several important advantages were assessed from the photometer. However, disadvantages were identified in the column flow and combuster surface effects.